I. Field of the Invention
The present invention relates to communication systems. More particularly, the present invention relates to a method and apparatus for determining to which user to provide access from among several users attempting to access a code division multiple access system.
II. Description of the Related Art
In accordance with several types of communication systems currently being used, access to the system is provided to one user at a time. Therefore, when a first user is granted access to the system, each other user must wait until the first user has released the system and access is granted to that user before he can use the system to communicate. Furthermore, in some such systems a scheduler is responsible for determining to which of the users access is to be granted. Each user applies to the scheduler for access to the system. The scheduler then selects from among the users that have submitted their applications.
In other systems, such as code division multiple access systems, access is granted to several users at once. In one such system, access is granted to users based upon several criteria. The first, and most important, criteria is to what type of service each user has subscribed. For example, in one such system, a user can request constant bit rate (CBR) service, variable bit rate (VBR) service, or available bit rate (ABR) service. Users that pay for CBR service are guaranteed to receive service at an agreed upon data rate (i.e., bit rate). In contrast, if a user pays for VBR service, the user will be provided service at the rate necessary to transmit the particular information that is being sent. In such cases, the user's fees are typically calculated based upon the rates that were requested and granted to the user. If the user pays for ABR service, then the user will be granted access and a data rate will be assigned on an “as available” basis. Therefore, if there is sufficient capability in the system to provide access to an ABR user, then the ABR user will be granted access.
The capability of the system is typically dependent upon whether the amplifier in the transmitter is capable of transmitting the ABR user's information with sufficient power without overdriving the amplifier in light of the amount of power required by each of the CBR and VBR user's power requirements. The data rate at which the access will be granted will depend upon the amount of power that is available for transmitting the ABR user's data.
One example of an ABR user is an Internet Service Provider (ISP). Since customers of an ISP are able to tolerate delays and lower data rates, ISPs typically will opt for the less expensive ABR service. Even so, there are frequently situations in which there is insufficient power to transmit data for all of the ABR users that are requesting ABR service at any particular point in time. Therefore, the transmitting station must determine to which ABR users service is to be provided.
Several techniques are known for determining how to select the particular user to whom access to a system should be granted in a shared access communication system in which access is granted to only one user at a time or to less than all of the users requesting service. Access to the system is provided by one or more channels (i.e., air interface links between a common transmitting station and the user) to the user. Accordingly, each user is associated with at least one channel. In a CDMA system, each channel is associated with a unique CDMA code. Typically, the condition (i.e., quality) of the channel directed to each user will vary over time. Furthermore, the condition of the channels will vary from user to user. In some systems, access is granted to the user that can most efficiently use the system (i.e., the user associated with the best channel and thus able to receive data at the highest rate), thus maximizing the throughput of the communication system (i.e., amount of data that can be communicated by the system within a predetermined amount of time). In other systems, access is granted such that each user will be provided with essentially equal access to the system when compared with the other users over a predetermined period of time. Equal access can refer to either the fact that each user gets an equal amount of time to communicate over the system, or that each user gets to transmit an equal amount of data over the system. Both the scheme in which the most efficient system user gets access and the scheme in which equal access is provided to each user are deficient. The scheme that focuses on maximizing throughput can lead to a situation in which some users receive little access to the system. In systems in which each user pays equally for access, this situation is unacceptable due to the resulting inequitable distribution of access. Likewise, in schemes in which each user is granted equal access regardless of the ability of that user to efficiently use the system, the throughput of the system suffers.
Accordingly, there is a need for a method and apparatus for determining to which user to grant access to a shared access communication system, such that the throughput of the system is maximized while ensuring that each user is granted equitable access to the communication system.